1. Field of the Invention
This invention relates to a method for making a semiconductor device and more particularly, to a method for making a semiconductor device adapted for use in the manufacture of solid-state image sensing devices of a backside illumination type.
2. Description of the Related Art
In recent years, solid-state image sensing devices, such as CCD (charge coupled device) image sensors, CMOS (complementary metal oxide semiconductor) image sensors and the like, have been mounted in and used for a variety of electronic apparatus.
The solid-state image sensing device, e.g. a CMOS image sensor, is composed of a photodiode wherein individual pixels are formed on a silicon substrate, and an on-chip lens for focusing light thereon. When incident light arrives at the photodiode through the on-chip lens, photoelectric conversion occurs to output a voltage value, thereby enabling light to be taken out as an electric signal.
With CMOS image sensors of a general construction, there are formed between the on-chip lens and the photodiode a transistor used for the input and output of a voltage, a wiring layer and the like in a multilayered fashion. This may lead to concern that incident light impinges on the wiring layer in the course of a light path and bounces off, or is turned owing to the inflection occurring at the interface with an interlayer film of the wiring layer, so that light focused with the on-chip lens cannot be efficiently arrived at the photodiode.
For this reason, there has been proposed adoption of a pixel structure of a so-called backside illumination type wherein incident light is illuminated from the backside of a silicon substrate to allow efficient arrival at the photodiode, unlike the above-stated pixel structure of the general construction (see Japanese Patent Laid-open No. 2007-258684).
FIG. 6 is a schematic view illustrating an example of a pixel structure of a CMOS image sensor of a backside illumination type. As shown in the figure, with the pixel structure of the backside illumination type, a wiring layer, not shown, is formed at one surface side (i.e. a lower side as viewed in the figure) of a silicon substrate 50 having a photodiode 51 formed therein. At the other side (i.e. an upper side as viewed in the figure) of the silicon substrate 50, a light-shielding film 53 is formed through a high-dielectric constant (high-K) insulating film 52 such as a hafnium oxide (HfO2) film, a silicon oxide (SiO2) film or the like. This light-shielding film 53 is so partly formed as to allow light to be passed to the photodiode 51 while shielding light at the other portions. An on-chip lens 56 is formed through a protective film 54 for planarization at a more incident side (i.e. a more upper side as viewed in the figure) of light than the light-shielding film 53. With this backside illumination type of pixel structure, light is illuminated from the back side (i.e. the upper side as viewed in the figure) of the silicon substrate 50, so that a quantity of the light entering the unit pixel is increased without undergoing an influence of the wiring and transistor, and a lowering in sensitivity relative to the change in incident angle of light can be suppressed.